Piano MEMS with hidden hinge

Abstract

The micro-electro-mechanical mirror device according to the present invention includes a platform pivotable about two perpendicular axes, and a hinge structure disposed beneath the platform. The hinge structure includes first and second hinges and a gimbal ring fabricated in a single layer beneath the platform layer. One end of the hinge structure extends from the undersurface of the platform, while the other end extends from a pedestal, which extends upwardly from a substrate.

1. A micro-electro-mechanical (MEMs) device comprising:
 a platform pivotable about first and second perpendicular axes above a substrate; 
 a pedestal extending upwardly from the substrate underneath the platform; 
 a first hinge extending from the pedestal enabling the platform to tilt about the first axis; 
 a gimbal frame extending at least partially around the first hinge for receiving an outer end of the first hinge; and 
 a second hinge extending from the gimbal frame to an underside of the platform enabling the platform to roll about the second axis; 
 wherein the first and second hinges are disposed entirely underneath the platform to enable adjacent MEMs devices to be closely packed together; 
 wherein the first hinge comprises a pair of serpentine torsional beams extending from opposite sides of the pedestal along the first axis into contact with the gimbal frame; and 
 wherein the second hinge comprises a pair of serpentine torsional beams extending from opposite sides of the gimbal frame along the second axis. 
 
   
   
     2. The device according to  claim 1 , wherein the gimbal frame and the first and second hinges have a same thickness and lie in a same plane, thereby enabling them to be fabricated from a same layer of material. 
   
   
     3. The device according to  claim 1 , further comprising:
 a first tilt electrode underneath the platform on one side of the first axis for tilting the platform about the first axis; and 
 a roll electrode underneath the platform on one side of the second axis for rolling the platform about the second axis. 
 
   
   
     4. The device according to  claim 3 , further comprising a second tilt electrode underneath the platform on an opposite side of the first axis for tilting the platform about the first axis. 
   
   
     5. The device according to  claim 3 , wherein the first tilt electrode is slanted relative to a bottom surface of the platform. 
   
   
     6. The device according to  claim 5 , wherein a portion of the bottom surface of the platform above the first tilt electrode is slanted. 
   
   
     7. The device according to  claim 3 , wherein the first tilt electrode comprises a two step electrode. 
   
   
     8. The device according to  claim 7 , wherein a bottom portion of the platform above the first tilt electrode includes a two stepped cavity. 
   
   
     9. The device according to  claim 3 , further comprising cross-talk shields extending from the substrate on either side of the first tilt electrode for minimizing cross-talk between adjacent electrodes. 
   
   
     10. The device according to  claim 9 , wherein the cross-talk shields also extend from a bottom surface of the platform on either side of the first tilt electrode. 
   
   
     11. A method of fabricating a micro-electro-mechanical device comprising the steps of:
 a) providing a silicon-on-insulator (SOI) structure comprising first and second superposed wafer structures separated by a first etch stop layer, each of the first and second wafer structures comprising a handle substrate, a wafer layer, and a second etch stop layer therebetween, wherein the wafer layers of the first and second wafer structures are disposed on either side of the first etch stop layer; 
 b) removing the handle substrate and the second etch stop layer from the second wafer structure of the SOI structure; 
 c) etching a gimbal frame, and first and second hinge structures from the wafer layer of the second wafer structure, including removing most of the first etch stop layer thereunder and therearound; 
 d) providing a substrate layer including a pedestal extending therefrom; 
 e) attaching the first hinge structure to the pedestal; and 
 f) removing the handle substrate and the second etch stop layer of the first wafer structure. 
 
   
   
     12. The method according to  claim 11 , wherein step a) includes providing a cavity in the first wafer layer above where the hinge structure is to be etched to ensure adequate spacing between the hinge and the first wafer layer. 
   
   
     13. The method according to  claim 11 , further comprising removing a triangular section from the first wafer layer, between steps c) and d), forming a slanted section therein. 
   
   
     14. The method according to  claim 13 , wherein in step d) the substrate layer also includes slanted electrode surfaces. 
   
   
     15. The method according to  claim 11 , further comprising removing rectangular sections from the first wafer layer, between steps c) and d), forming a stepped section therein. 
   
   
     16. The method according to  claim 11 , wherein step c) includes etching the first hinge a pair of serpentine torsional beams extending inwardly from the gimbal frame along a first axis; and etching the second hinge into a pair of serpentine torsional beams extending outwardly from opposite sides of the gimbal frame along a second axis. 
   
   
     17. The method according to  claim 11 , wherein step c) includes etching crosstalk shields from the wafer layer of the second wafer structure proximate outer edges of the wafer layer of the first wafer structure. 
   
   
     18. The method according to  claim 11 , wherein in step d) the substrate layer also includes cross-talk shields extending upwardly proximate outer edges thereof.